In this episode of "The Show with the Mouse," moderator Armin explains how a catalyst works. Especially in cities the streets are full of cars. They are gathering at traffic lights, drive around and permanently blow harmful exhaust fumes into the air. To ensure that as little as possible of these exhaust gases leave the exhaust, cars are equipped with catalysts. The program shows how a catalyst is built - and how it can help reduce the pollution of the air.